Assessment on the Effective Green-Based Nepal Origin Plants Extract as Corrosion Inhibitor for Mild Steel in Bioethanol and its Blend

Effects of Nepal origin plant species of Vitex negundo, Catharanthus roseu, Aegle marmelos and Elaeocarpus ganitrus extracts on mild steel corrosion were explored in bioethanol (E100) and its blend (E15) in airtight condition at 25±2 °C using static immersion, inhibition efficiency and mechanism tests which were complemented with adsorption isotherms and potentiodynamic polarization studies. Corrosion resistance of the mild steel was increased with increasing 500-2000 ppm concentrations of each plant extract in E100 and E15 biofuels. Additions of V. negundo and C. roseus extract separately in both the biofuels seems to be more effective inhibition actions to prevent the mild steel corrosion than A. marmelos or E. ganitrus addition so as the corrosion rates of the mild steel in E100 and E15 are successfully lowered even than in commercial gasoline (E0). The results obtained from the corrosion rate revealed the order of the corrosion inhibition efficiency (IE) as V. negundo > C. roseus > A. marmelos > E. ganitrus. The maximum IE (IEmax) in V. negundo and C. roseus leaves was showed about 89-86% and 71-75%, respectively, at 2000 ppm concentration, in spite of the other two more plants leaf extract also used as the corrosion inhibitors for the mild steel in both E100 and E15 biofuels. The IE increased on increasing inhibitor concentration following the Langmuir and Temkin adsorption isotherms but decreased with immersion time which suggested that the corrosion inhibition mechanism is of physical type of adsorption of the leaves constituents on the mild steel surface. A. marmelos extract acted as an anodic type of inhibitor in E100 and E15, while E. ganitrus acted as mixed